The most common power cycle currently employed using natural gas fuel is the gas turbine (GT) in combination with a heat recovery steam generator (HRSG). Such system may be referred to as a natural gas fired combined cycle (NGCC) wherein an advanced steam Rankine cycle power generation system (HRSG plus steam turbines) utilizes the hot turbine exhaust heat to form steam for further power generation. An NGCC unit is typically understood to be a highly efficient method of power generation utilizing predominately natural gas fuel. In use of an NGCC unit, all CO2, water vapor, and oxides of nitrogen (NOx) derived from combustion are vented to the atmosphere.
Utilization of CO2 (particularly in supercritical form) as a working fluid in power production has been shown to be a highly efficient method for power production. See, for example, U.S. Pat. No. 8,596,075 to Allam et al., the disclosure being incorporated herein by reference, which describes the use of a directly heated CO2 working fluid in a recuperated oxy-fuel Brayton cycle power generation system with virtually zero emission of any streams to the atmosphere. It has previously been proposed that CO2 may be utilized as a working fluid in a closed cycle wherein the CO2 is repeatedly compressed and expanded for power production with intermediate heating using an indirect heating source and one or more heat exchangers. See, for example, U.S. Pat. No. 8,783,034 to Held.
Various means have been pursued for increasing efficiency in such power productions methods. For example, recuperative heat exchanger optimization has been pursued, such as via hot gas compression or through external heat sources. Optimization of CO2 cycles has often focused on maximizing turbine power output. Despite such efforts, there remains a need in the field for power production systems and methods with increased efficiency and power output while limiting or substantially avoiding emission of any streams (e.g., CO2, NOx, and other combustion-related products) to the atmosphere.